Integrated closed loop control method and apparatus for combined uninterruptible power supply and generator system

ABSTRACT

The present invention provides a method, computer program product, and apparatus and control system and method for providing substantially uninterrupted power to a load. The apparatus includes a control system coupled with an electrical power storage subsystem and a electrical power generator. The control system is configured to provide a plurality of modes of operation including at least a static compensator (STATCOM) mode, an uninterruptible power supply (UPS) mode and a generator mode (gen set), and to control transitions between each of the plurality of modes. In one embodiment, the control system is an integrated closed loop control system that includes a current control system and a voltage control system. The apparatus is capable of operating at least two of the plurality of modes simultaneously, including ramping the gen set mode up and simultaneously ramping the UPS mode down as the gen set mode is ramped down.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. 119(e)to U.S. Provisional Application No. 60/431,464 filed 06 Dec. 2002entitled Integrated Closed Loop Control Method And Apparatus ForCombined Uninterruptible Power Supply And Generator System; whichapplication is incorporated herein by reference.

FIELD OF THE INVENTION

This invention pertains generally to control systems, and moreparticularly to control systems allowing plug-and-play integration ofmodules in a power conditioning system.

BACKGROUND

There are different devices known in the art for improving power qualityand reliability of grid or utility line power supplied to sensitiveloads. Three of these include, a static compensator (STATCOM), anon-line uninterruptible power supply (UPS), and an off-line UPS. A UPSmay also be operated in cooperation with a power generator or gen set,for long term interruptions.

FIG. 1A illustrates a typical STATCOM 100 in which a Voltage SourceConverter (VSC) 102 is connected to an AC system 104 supplying a load106 through a shunt-connected transformer 107. A capacitor 109 isconnected to the DC terminals 108 of the VSC 102 and is usually anintegral part of the VSC 102. The VSC 102 controls the line voltage byinjecting or absorbing reactive power. A STATCOM aids in controllingload voltage fluctuations that result from a load's transient orchanging reactive power requirements. While a STATCOM has relatively lowoperation costs, a STATCOM does not provide active power and thereforefails to operate under short circuit conditions or other conditionswhere active power provision is required or desired. Further, a STATCOMhas a limited ability to correct voltage fluctuations due to grid faultsor switching events.

FIG. 1B illustrates a block diagram of the main components of anexemplary on-line UPS system 110. This UPS system 110 is on-line duringnormal operation, where on-line operation includes converting energyfrom a grid or utility 112 through a rectifier 114 from AC to DC,maintaining a battery 116 at full charge, and converting the energythrough an inverter 120 to an AC-system resulting in double conversion.A static bypass switch 123 and the mechanical bypass switch 124 arenormally open. The UPS system 110 typically operates such that it issynchronized with the bypass source 126 or with the grid 112. A chemicalbattery 116 is used as energy storage for bridging outages. In case of amalfunction of the system 110 the mechanical switch 124 allows operationby connecting the grid 112 or bypass supply 126 directly to the load130. In case of a malfunction on the load assembly, the static bypassswitch 123 is closed to increase short circuit capability for fusecoordination. In case of a malfunction on the grid, the rectifier 114 isblocked and energy is taken from the battery 116 without disturbances onthe load 130.

The on-line UPS 110 requires double conversion resulting in relativelylow efficiency and high operation costs. Further, the grid 112 isdecoupled from the load and, thus, there are no transients on the loadvoltage under grid disturbances. Short circuit capability is provided byclosing the static bypass switch 123.

FIG. 1C illustrates a block diagram of the main components of a typicaloff-line UPS 140. The off-line UPS 140 is off-line during normaloperation, where off-line operation provides that a solid state breaker(SSB) 122 is closed, a mechanical bypass switch 124 is open, and astatic converter 142 maintains a battery 116 at full charge. A chemicalbattery 116 is typically used as energy storage for bridging outages.Outage and sag conditions on the grid must be detected and compensatedfor fast in order to protect the load or load assembly 130. In case of amalfunction on the load assembly 130, the SSB 122 remains closed to makeuse of the grid short circuit capability for fuse coordination. In caseof a malfunction of the off-line UPS system 140, the mechanical bypassswitch 124 allows operation by connecting the grid 112 directly to theload 130. In case of a malfunction on the grid, the SSB 122 will beopened and the converter 142 supplies the load. The off-line UPS 140operates at relatively low operation costs. The grid 112 is coupled tothe load 130, thus, grid disturbances are transferred to the load 130under standby conditions (normal operation) until the SSB opens.

FIG. 2 shows a block diagram of a UPS system 148 having an off-line UPS150 in cooperation with a power generator or gen set 152 for long terminterruptions. The off-line UPS 150 consists of a converter 154 and anenergy storage device 116, such as, for example, a chemical battery, anarray of chemical batteries, or other storage devices or systems. Theconverter 154 provides fast dynamic behavior. The converter powersemiconductor(s), typically used in the converter, however, have no orsubstantially no overload capability. An accompanying UPS control system(not shown) provides for operation of the switch 156 in the event of anoutage or sag, and for proper charging of the battery.

For long term interruptions the independent gen set 152 is connecteddirectly to the load side of the AC-system. The gen set 152 consists ofa power source (such as, for example, a natural gas, diesel engine,gasoline engine or other engine) and a mechanical to electricalconversion device (i.e. a generator). An accompanying gen set controlsystem (not shown) controls the torque and the speed of the shaftproducing active power. In the conventional off-line lPS with anindependent gen set, the gen set control system does not cooperate withthe UPS control system. The shaft speed (for example revolutions persecond) routinely corresponds to the electrical system frequency (forexample, cycles per second or hertz). Typically, the gen set has a longresponse time to dynamic voltage (or current) variations and a largeoverload capability. The long response time is a result of theelectromechanical and the power generation process with its rotatingmass or momentum. System resonance frequencies in the area of a fewHertz are usual.

The gen set 152 and the UPS 150 each typically have their ownindependent closed loop control unit (not shown). The operationprinciple of the UPS system 148 provides for the operation of the twoindependent gen set 152 and UPS 150 devices in the following way:

-   -   1. Standby Mode: gen set 152 is not in operation, and UPS 150 is        in standby mode, but is not exchanging power with the load (it        may be maintaining the storage charge). System 148 control        system (not shown) monitors the grid voltage. The switch 156 is        closed.    -   2. Disturbance on the grid side: The system 148 initiates the        switch 156 to open; the load 130 is taken over by the UPS 150        (island mode); and depending on the energy content of the        storage device 116, the gen set 152 is started.    -   3. If the interruption is only short term: the system 148        initiates the switch 156 to close; load 130 is handed over to        the grid 112; the storage device 116 is charged; and transfer        back into standby mode; gen set 152 is not in operation.    -   4. If the interruption is long term: the system 148 transfers        from the UPS 150 to the gen set 152; UPS system 150 remains in        standby mode; and switch 156 is open.    -   5. When the long term interruption ends: the system 148        initiates the switch 156 to close; and the load 130 is        transferred to the grid 112.

In the case of a long term operation, the gen set 152 provides theactive power to the load. The operation of this UPS system 148 allowsfor one of either the gen set 156 or the UPS 150 to operate at any giventime. There is no common control or coordination or simultaneousoperation, only separate individual control of the gen set and UPS withsequential operation of each. The drawback of this operation principleis that the good dynamic behavior of the UPS (that is, rapid response toreactive or active power variations in the load and stabilization offrequency), especially during generator operation, cannot be used orachieved because there is no common control unit available.

The standby gen set provides limited dynamic behavior during start up,even if it is a diesel gen set (DGS) of the fast starting/running type(for example, of the type running at 1800 rpm), with lubrication systemheating. In these systems the starting phase may typically last 5 to 8seconds until nominal speed (no-load) has been reached after which onemay switch in load elements.

DGS load connection or switch-in as well as rejection produce speed andfrequency deviations requiring at least 2 to 5 seconds until frequencydeviation has reached a steady state value (for example, made up ofcontrol dead time, fuel injection time constant and settling time). Inthe case of start up, this period must be added to the 5 to 8 secondsrequired for attaining nominal speed, as described above so that thetotal time for startup and stabilization may be at least 7 to 13 secondsor more. FIG. 3 shows a typical frequency 160 behavior during loadswitching. Typical frequency deviation resulting from speed deviationcaused by load change (switch-in and rejection) of a standby diesel genset. The so-called dynamic deviation depends on the:

-   -   Inertia (the rotating mass of the engine): small inertia        large excursion.    -   Turbo-charging: the higher the charging degree        the larger the deviation.    -   Size of loads subject to switching: the larger the load size        the larger the deviation.

Frequency deviations (typically approximately 10% of rated frequency, orabout ±6 Hz for 60 Hz operation or ±5 Hz for 50 Hz operation) lastingseveral seconds may cause trouble or even damage to frequency dependentloads like computer screens, TV sets and other such devices. Note thatin nominal conventional grid connected power systems the steady statefrequency deviation is held within ±0.1 Hz and that at frequencies below58.5 Hz (that is, at a drop of 1.5 Hz) of system frequency (60 Hz) loadshedding occurs.

Load takeover normally takes place stepwise (for example, in three 3steps) due to the limited size of the diesel and gen-set (for economicreasons the equipment is usually sized not much larger than the load) aswell as due to drastic speed deviations (and therefore drastic frequencyexcursions), as discussed above.

In order to avoid the frequency deviations and load takeoverrestrictions described above, system designers could specify a gen setsize that is as much as five times larger than the load, with resultingeconomic penalties.

If a voltage source converter (VSC) is employed for the converter 154then STATCOM operation is possible, exchanging reactive power, andabsorbing active power to cover the losses. However, in conventional UPSplus gen set systems, the full functional advantages of using afour-quadrant voltage source converter (VSC) during transfer to andsubsequent operation of the gen set are not realized at least since theindividual UPS and gen set controls are not cooperated. Conventionalcontrol systems do not provide system designers as much incentive orflexibility to choose the VSC for the converter (see FIG. 2) since theVSC's full capabilities are not engaged by the available conventionalcontrol system technology.

SUMMARY

The invention provides an apparatus and method of providinguninterruptible power supply (UPS) capability or operating modeutilizing a voltage source converter (VSC), a source of stored energy,and/or generation together with an integrated cooperative controlsystem. The invention provides for superior performance characteristicsover a conventional uninterruptible power supply (UPS), and may be usedfor both critical loads or for stabilizing critical components in theelectrical transmission and distribution grid. Method and apparatusperformance improvement and optimization or near-optimization isachieved in both system hardware that provides the uninterruptible powersupply and other component choice and operation. In particular, theinvention makes it possible to fully utilize a voltage source converter(VSC) for the converter component of a conventional UPS to provide theUPS mode of operation without requiring all of the hardware and controlof conventional UPS systems. Furthermore, with a VSC deployed, theinventive control method and apparatus enable a UPS to simultaneouslycontrol a load voltage while supplying load power, by independentlyinjecting or absorbing both active and reactive power. Moreover, VSCfunctionality is preserved during transitions from one mode of operationto another, and during operation of an optionally connected generatorset.

In one embodiment, in the event of a long term interruption, a powergeneration module, such as a gen set, supplies the power to the load.During this period, the inventive UPS operates in a standby mode, but isactively exchanging reactive and active power, as well as recharging astorage device as needed. In standby or charge mode the UPS continues toinject and absorb reactive power. Thus both systems, the UPS as well asthe gen set, are in operation. In one embodiment, the overall apparatusis optimized by providing a control system and method for simultaneouslyand jointly controlling the UPS and the gen set in all operating modesas a single cooperative closed loop control.

Thus, the inventive method and apparatus result in superior performanceover conventional systems and methods, by operating the UPS as a staticcompensator (STATCOM) throughout the entire event duration, whethershort or long term, to respond to the load's reactive powerrequirements. Embodiments of the novel method and apparatus, further,perform dynamic load leveling by providing or absorbing active power,improving and usually optimizing dynamic behavior under islandconditions (where the load is isolated from the power grid and maysharply vary over short time periods), and optimizing or nearlyoptimizing behavior during transitions including load pick up by theUPS, hand off between the UPS and gen set, and re-synchronization to thegrid. The inventive method may advantageously be implemented as acomputer program and computer program product executing on or in ageneral or special purpose computer having a processor for executingcomputer instructions and a coupled memory for storing data,instructions, and commands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a block diagram of the main components of a conventionalstatic compensator (STATCOM).

FIG. 1B depicts a block diagram of the main components of a conventionalon-line uninterruptible power supply (UPS).

FIG. 1C depicts a block diagram of the main components of a conventionaloff-line UPS.

FIG. 2 depicts a block diagram of a conventional UPS system having anoff-line UPS in cooperation with a power generator or gen set for longterm interruptions.

FIG. 3 depicts a typical frequency behavior during load switching.

FIG. 4A depicts a simplified block diagram of an exemplary embodiment ofthe inventive power source apparatus or system.

FIG. 4B depicts a simplified block diagram of another embodiment of theinventive power source apparatus or system.

FIG. 4C depicts a simplified block diagram of another embodiment of theinventive power source apparatus or system.

FIG. 5 depicts a simplified block diagram of another general embodimentof the inventive power source apparatus or system.

FIG. 6 depicts a simplified block diagram of another embodiment of theinventive power source apparatus or system with integrated voltagesource controller.

FIG. 7A depicts a simplified block diagram of another embodiment of theinventive power source apparatus or system with multimode control andoperation.

FIG. 7B depicts a simplified block diagram of another embodiment of theinventive power source apparatus or system.

FIG. 8A depicts a simplified block diagram of one implementation of oneembodiment of the inventive power source apparatus or system withmultimode control and operation.

FIG. 8B depicts a simplified block diagram of one implementation of oneembodiment of the inventive power source apparatus or system withmultimode control and operation.

FIG. 9A depicts a simplified flow diagram of one embodiment of thecontrol modes, the transitions between modes, and parameters associatedwith the modes.

FIG. 9B depicts a simplified flow diagram of another embodiment of thecontrol modes, the transitions between modes, and parameters associatedwith them.

FIG. 10 depicts a simplified block diagram depicting one implementationof one embodiment of the converter current controller.

FIG. 11 depicts a simplified block diagram depicting one implementationof one embodiment of the converter voltage controller.

FIG. 12 depicts a block diagram of one implementation of one embodimentof the detection and mode selection unit.

FIG. 13A depicts a simplified block diagram of one implementation of oneembodiment of the inventive power source apparatus or system with a SMESenergy source.

FIG. 13B depicts a simplified block diagram of one implementation of oneembodiment of the inventive power source apparatus or system with aflywheel energy source.

FIG. 14A shows a graphical representation of the three phase gridvoltage with the voltage sag.

FIG. 14B shows the graphical representation of the three phase loadvoltage during the voltage sag.

FIG. 14C depicts a graphical representation of the amplitude of the gridvoltage and the load voltage showing the system's rapid response to thesag.

FIG. 14D depicts a graphical representation of the three phase loadcurrents.

FIG. 14E depicts a graphical representation of the three phasecompensation currents supplied by VSC and storage supply to the load.

FIG. 15A graphically depicts the load voltage as the voltage supplied toload transitions from the VSC to the gen set.

FIG. 15B graphically depicts the amplitude of the grid voltage and theload voltage as the gen set takes over and supplies power to the load.

FIG. 15C graphically shows the three phase load current as the gen settakes over.

FIG. 15D graphically shows the three phase VSC current as the loadsharing ramps down the VSC.

FIG. 15E graphically shows the three phase generator current as the loadsharing ramps up the gen set current supplied to the load.

DETAILED DESCRIPTION

The novel method and apparatus of the present invention, in oneadvantageous application, provides power to normal electrical loads andmore especially to sensitive loads, such as semiconductor manufacturingplants, data centers, Internet or data server farms, and other sensitiveloads, even under voltage disturbances and interruptions on the gridside.

As shown in FIG. 4A, the Voltage Source Converter (VSC) 240 of a staticcompensator or STATCOM, can be connected to an energy storage device1000 at the direct-current or DC terminals 208 of the VSC 240. The VSC240 can draw real power from the energy storage device 1000 and deliverit as alternating-current or AC power to provide temporary systemsupport. The VSC 240 can also control the line voltage by injecting orabsorbing reactive power. The VSC can also control energy absorptionfrom the AC system to keep the energy storage device charged.

FIG. 4B depicts a block diagram of one embodiment of a power system 220in accordance with the present invention in which the power system 220includes a plurality of modules. The power system 220, for example,includes an AC interconnection module 1020, a power conditioning module1010, system controls 221 which in at least this embodiment are a set ofintegrated cooperating system controls, and an energy storage module1000. The set of integrated cooperating system controls mayadvantageously be implemented as a computer program on a general orspecial purpose computer. Additional implementations and embodiments ofembodiments of the integrated cooperating system control are illustratedand described relative to FIGS. 8-9 and elsewhere in the specification.The power system 220 is designed to provide real and reactive power forload 222 during short-term interruptions of utility 224. Power system220 operates off-line. When a voltage disturbance is sensed on grid orutility 224, the system 220 creates a complete disconnect from grid orutility 224 and provides back up power to the load 222 via the energystorage module 1000. The power system 220 provides performancecharacteristics of both a static compensator (STATCOM) and aconventional off-line uninterruptible power source (UPS), operating incooperation.

The overall system and method of operation and control as well as ofindividual modules are preferably technology independent—that is,applies to various technologies without limitation. The energy storagemodule 1000, for example, may be implemented by batteries, fuel cells,superconducting magnets (SMES), electrochemical capacitors, flywheels,other energy storage mechanisms, systems, or methods known in the art,or any combination of these energy storage mechanisms, systems, ormethods. The power conditioning module 1010 and static isolation switch1040 with a bus reactor in the AC connection module 1020 areadvantageously implemented with solid-state technology and physicaldevices, but one skilled in the art would recognize that othertechnologies may be utilized to implement these features to achieve thedesired operation and function.

FIG. 4C depicts an alternative embodiment of a power system 220 thatfurther includes a power generation module 1030 to provide power forlonger duration interruptions. Again, when a voltage disturbance issensed on grid or utility 224, the system 220 creates a completedisconnect from grid or utility 224 and provides for a full ramp-up ofthe back up power generation source to the load 222. The system providesthe performance characteristics of a static compensator (STATCOM) and aconventional off-line uninterruptible power source (UPS) as well as analternative power generation source, operating in cooperation. Forexample, the inventive control methodology and apparatus achievesSTATCOM performance characteristics during both transitions to andoperation in generation mode as well as in other operating modes. Asdescribed above, the overall system and method and individual modulesand module methodology are advantageously technology-type independent.

The power generation module 1030, for example, may be implemented bycombustion turbines, micro-turbines, diesel gen sets (AC- orDC-connected), internal combustion (IC) engines, fuel cells, and otherpower generation mechanisms known in the art, or any combination ofthese technologies. A diesel gen set, as used herein and as known in theart, is for example a combination of a diesel engine (or other primemover) and an electrical synchronous generator (or other converter fromkinetic energy to electrical energy). It is to be understood that thegeneration module 1030 is optional and allows the system to providepower from a dedicated fuel supply (of whatever type) during longerduration power interruptions. Without the generation module, the powersystem 220 may still provide real and reactive power for shorter-terminterruptions.

A control module for a power system is provided to activate and regulateone and, more often, a plurality of modules comprising the power system,such as a power system 220 shown in FIG. 5 comprising power electronics,energy storage and alternative power generation. In the power system 220shown in FIG. 5, for example, a control module 221 interacts with theplurality of power system modules including an energy storage module1000, a power conditioning module 1010, an AC interconnection module1020, and an optional generation module 1030 (shown in the FIG. 5embodiment as an optional DC-connected generator 1032). Power system 220with control module 221 operates off-line and is advantageously capableof accommodating power levels at any range within the 5 to 40 MW rangeand operating at the electrical substation level. However, in light ofthe description below, it is to be understood that embodiments of theinvention may apply to a variety of power levels including ranges below5 MW and above 40 MW as well as within the range between 5 MW and 40 MW.

Power system 220 may also provide reactive support of electrical systems(or VAR support). To provide VAR support, for example, a STATCOM, orstatic synchronous generator utilizing a voltage source converter (VSC)may be provided, as shown in the embodiment of FIG. 6. FIG. 6 depicts anexemplary power system 220 comprising a STATCOM utilizing VSC 240 inseries with solid state breaker (SSB) 262, and control system 221.Energy storage module 1000 is connected to VSC 240. During systemtransients, such as generation-rejection and/or load-rejection, the VSC240 capabilities are to be utilized to support the load assembly withinthe specified capabilities of the converter. Further, FIG. 6 depicts twoembodiments of generation module 1030—an AC-connected gen set 1031 and aDC-connected gen set 1032. The use of a DC-connected gen set requiresadditional controlled rectifier 1080. The main advantages of aDC-connected generator over an AC-connected generator include: nogen-set synchronization prior to load take-over (quicker load pick up),reduced impact to remaining loads upon sudden changes in load, andsimpler coordination between storage system and prime mover.

Various specific embodiments of the different modules discussed abovehave different specific control variables and control systems. In oneembodiment, for example, the control module 221 includes a base systemcontrol module and one or more device-specific modules that individuallyor collectively correspond to one or more of the individual power systemmodules, for example the energy storage module 1000, the powerconditioning module 1010, the AC interconnection module 1020, and thegeneration module 1030. Thus, in addition to the system 220 allowing fortechnology independent modules to be used, the control system includesindependent control modules designed to control a particular module ordevice of the system 220. If the energy storage module 1000 includesbattery energy storage (BES), an individual control module specificallydesigned to control the BES can be used along with the base systemcontrol module of the control system 221. If the energy storage module1000 includes a superconducting magnetic energy system (SMES), however,the control system includes a different module designed to control theSMES, and so forth.

In one embodiment the individual modules of the system 220, includingfor example the modules of the control module 221, are advantageouslybut optionally designed to allow for “plug-and-play” interchanging ofcontrol modules. In this embodiment, the control module 221 enablesdifferent system applications to be implemented by “plugging” variousalternative control modules into a base system control module, andsetting the module-specific variables and/or parameters or controlvalues and rules. “Plugging” for the purpose of the present inventioncan include specially designed hardware and/or software that may bephysically plugged into or otherwise operatively connected to or coupledwith a base system control, or the base system control module mayinclude standard hardware and/or software that may be reprogrammed orselected from a menu of options for a particular module or device of thesystem. Thus, a plug-and-play base system control module allows forpossible expansion, reduction, or exchange of control modules asdictated by the primary configuration of the system 220. It alsofacilitates maintenance with little or no disruption of operation ordown time.

One particularly advantageous embodiment of power system 220 is shown inFIG. 7A, utilizing lead-acid battery 1060 as energy storage module 1000and a DC-connected Gen set 1032 as generation module 1030. Controlmodule 221 advantageously incorporates mode selection unit 1080, basesystem control module 1090, energy storage control module 2000, andalternative power source control module 2010. An alternative embodimentshowing a DC-connected generator is illustrated in FIG. 7B.

In this embodiment, the energy storage control module 2000 is a batteryenergy storage (BES) control module, and the alternative power sourcecontrol module 2010 is suitable for control of a DC-connected Gen set1032, as depicted. As described above, the individual control modules2000 and 2010 are optionally plug-and-play modules that may beinterchanged as needed. Thus, if the battery 1060 in the system isreplaced by another different energy storage device, such as an SMESdevice, the battery energy storage control module may be replaced(either with a new hardware and software control module or byreprogramming the control module) with an alternative energy storagecontrol module that is specifically designed to control the SMES device.Similarly, if a different type of battery is used, such as a SodiumSulfur battery, the battery energy storage control module may bereplaced or reprogrammed to provide the specific charge and dischargecontrol needed by the Sodium Sulfur battery. Control modules mayalternatively be universal and switched between programs or modes tosuit the present application. It is to be understood that FIG. 7Aillustrates one embodiment of the inventive system for the purposes offurther specific discussion, and that the inventive concept, system, andmethod are applicable to a variety of specific embodiments.

Battery energy storage control module 2000 may include batterysupervision and battery management systems to be provided by thechemical battery supplier. These features may desirably incorporatebattery-type and battery-cell specific knowledge for beneficial usageand prolonged life time. Battery conditioning in the form of specificcharge and discharge treatment is advantageously but optionallyimplemented in the charge-control and discharge-control functions of thecontrol system. Charge and discharge control function parameters areavailable, for example, in form of battery models, charge and dischargecharacteristics, or other characteristics as needed for control of thebattery and as known in the art.

Diesel Gen sets, such as Gen set 1032, are known in the art, having acontrol package reflecting Start/Stop controls, fuel injection system,and generator excitation control. The interface and signal exchange aredefined in the context of the components and operation controls present.The DC connection of Diesel Gen set as such requires a rectifier, suchas rectifier 1081, for which control system 221 incorporates controlmeans to provide the required steady state and transient performance.

FIG. 7B depicts another advantageous embodiment of the DC connection ofa generation module, in which a controlled, solid state breaker 1035 isutilized to bypass rectifier 1080, storage module 1060, and converter240 in the event that additional fault clearing current is needed tooperate fault clearing devices in the connected load 222. Solid statebreaker 1035 is controlled by control system 221 and is closed toprovide a temporary AC-connection for the gen set 1032 in the event of afault on the load side. After the fault has cleared breaker 1035 isre-opened and the system returns to normal operation.

FIG. 8A depicts a block diagram of one embodiment of a power system 220with multimode control and operation facilitated by control system 221,comprising battery 1060 as energy storage module 1000, and anAC-connected Gen set 1031, with associated packaged generator controls1033, as generation module 1030. Portions of the control structuredepicted correspond to the individual control modules shown in FIG. 7A.Energy storage control module 2000 comprises DC link voltage control 241and storage control unit 247. For an electrochemical battery controlunit 247 may advantageously comprise, FIG. 8B, a battery voltage controlunit 244, switch 246, battery current control 245, and batterymanagement system 243. STATCOM (VSC) control module 1090 comprisesseveral control units including load sharing control 281, referencevalue generator 248, Q-control 242, a current control system 223including VSC current control 230, a voltage control system 225including VSC voltage control 232, and pulse pattern generation unit252. The alternative power source control module 2010 in oneimplementation of this embodiment comprises controls 1033 associatedwith the AC-connected gen set 1031 including a synchronizing unit 285,generator excitation control 282, diesel control system 552, dieselstart/stop unit 550, and fuel injection system 554. The control unitscomprising the alternative power source control module 2010 aretypically determined by the type of power source employed, and are knownin the art. Control system 221 is advantageously capable of interfacingwith alternative power source control module 2010. The energy storagecontrol module 2000, the STATCOM control module 1090, the sag and outagedetection module 1080, and the alternative power source control module2010 are advantageously further designed to allow for “plug-and-play”interchanging of the control modules with the control system 221, orreconfiguration within a specific control module, so that the controlsystem 221 may be easily modified if any of the system modules are addedor removed from the system 220.

FIG. 8B depicts another embodiment of the control structure in the casewhere a DC-connected gen set serves as generation module 1030. Thecontrol structure is similar to that illustrated and described relativeto FIG. 8A, and further includes the alternative power source controlmodule 2010, comprising rectifier control 3030 and rectifier pulsepattern generation unit 3031 associated with additional rectifier 1080.As for the AC-connected gen set embodiment with an electrochemicalbattery, energy storage control module 2000 comprises battery voltagecontrol unit 244, switch 246, battery current control 245, and batterymanagement system 243. Further, in the case of a DC-connected gen set asin FIG. 8B, synchronizing unit 285 and load sharing control, depicted inFIG. 8A, are unnecessary. The energy storage control module 2000, theSTATCOM control module 1090, the sag and outage detection module 1080,and the alternative power source control module 2010 are advantageouslyfurther designed to allow for “plug-and-play” interchanging of thecontrol modules with the control system 221, or reconfiguration within aspecific control module, so that the control system 221 may be easilymodified if any of the system modules are added or removed from thesystem 220.

Power source system 220 is configured to compensate for voltagedisturbances and power interruptions on a power grid or utility line 224by providing power to one or more loads 222 when a disturbance orinterruption occurs. The apparatus employs a multimode control system221 which allows the power source system 220 to cooperate and control aplurality of operational modes. In one embodiment, the system 220 iscapable of either injecting or absorbing reactive power thus operatingas or substantially as a static compensator (STATCOM mode) withoutactually having the structure or components of a conventional staticcompensator or STATCOM. The system 220 and associated method is furthercapable of at least compensating for short term voltage disturbances andpower interruptions, in effect, operating as an uninterruptible powersupply (UPS); and further the system and method are also be capable ofsupplying longer term power to the load through an electrical generatorsuch as an engine-driven electrical generator (gen set). The controlsystem 221 and method may advantageously be included within power sourcesystem 220 which provides functionality and control for system 220 tooperate in any one of or combination of the plurality of operationalmodes as well as controlling transitions between operational modes. Thecontrol system enables two or more modes to operate at the same time toprovide more stable power to the loads. The controlled transitionsbetween operational modes greatly improves the reliability of the powerreceived by the load. Furthermore, continuity of operation of highlysensitive loads is assured. Thus, the power source system 220 maintainspower sensitive loads, such as semiconductor manufacturing facilities,other manufacturing facilities, data service centers, server farms,hospitals, emergency centers or other sensitive loads, withuninterrupted power.

The control system 221 provides for continuous uninterruptible powersupply and/or generation by means of an integrated, cooperative controlscheme. The control system 221 enables operation of a voltage sourceconverter (VSC) 240 simultaneously with a source of stored energy(storage module 1000) and alternate power generation system 1030 tocontrol the load voltage (frequency and amplitude) by injecting orabsorbing both active and reactive power during all operating modes.Injection or absorption of real or reactive power are determined by theneeds of the load 222 as well as any applicable performance limitationsof the subsystems, for example, the available capacity of storage module1000.

The multimode control system or integrated closed loop control 221provides control for the STATCOM, UPS, and gen set modes of operation.In one embodiment, either the current control 223 or the voltage control225 is activated at one time, such that the current control 223 isactive when the system 220 operates in standby mode, charge mode, anddischarge mode with the gen set. The voltage control 225 is active indischarge mode without the gen set. The control system 221 providesoptimal power (or near optimal power) to a load by coordinating theoperation of the plurality of modes, including operating two or moremodes simultaneously.

The control system 221 provides for operation of power system 220 in oneof three modes—standby mode, discharge mode, or charge mode—as well asfor minimally disruptive transitions between and among any of thesemodes. The control system 221 allows the power system 220 to act eitheras a current source or a voltage source. When acting as a currentsource, for example, the control system 221 allows for simultaneouslysharing the load 222 among multiple energy sources, for example ageneration module 1030, such as gen sets 1031 or 1032, and a storagemodule 1000 such as a battery 1060.

FIG. 9A depicts a simplified flow diagram 700 of the control modesaccording to one embodiment of the invention, the transitions betweenand among modes, and parameters associated with the modes. Specifically,FIG. 9A depicts modes supported by control system 221 in an embodimentof power source system 220 comprising an AC-connected gen set, such asthe embodiment depicted in FIG. 8A.

The control system operates generally as follows. During normaloperation of the grid or utility 224, power system 220 is operated inmode A, stand-by mode (block 710), acting as a STATCOM, and voltagesupport is provided by VSC 240.

When the interconnected utility grid is unable to supply proper power(voltage, current or combination of voltage and current), the controlsystem operates in mode C, discharge mode (block 714), providing powerto the load from the storage unit 1000 and/or alternative powergeneration, such as the AC-connected gen set 1031 in one embodiment. Inthis mode the control system operates to provide a full alternativepower supply.

More specifically, in the event of a grid 224 fault, that is when thegrid is unable to supply a proper voltage, current, or powerrequirement, the power system 220 enters mode B (block 712), atransition mode between standby and discharge modes. In this transitionmode, referring to FIG. 8A, the SSB 262 via the Sag and Outage Detectionmodule 1080 is commanded to disconnect the load 222 from the feeding busand supply it from the energy storage module 1000, such as battery 1060,within a specified time frame. In discharge mode, block 714, the storagemodule 1000 supports the load 222 for a period of time, after which timethe load 222 will be transferred to the alternative power source duringmode D (block 716), a transition between discharge and alternative powersource generation mode (block 720). In block 720, then, power to load222 is supplied by the generation module 1030, such as gen set 1031, ifa generation module is included in power source system 220. The powersystem 220 transformer advantageously remains energized at all times toachieve fast response and to recharge energy storage module 1000utilizing VSC 240. The energy for recharging storage module 1000 mayeither be derived from the main power source, for example from theutility 224, or from the alternative power source in the generationmodule 1030, such as gen set 1031. If a generation module 1030 is notincluded in power system 220, control system 221 issues a set ofcommands to disconnect the load after a period of time in dischargemode. If power transfer to the generation module 1030 is not necessary,control module 221 resynchronizes the load 130 to the recovered utility112 (see return to grid block 722).

For further clarification purposes, FIG. 9B is provided to illustrateoperating modes and transitions of another embodiment of control system221, specifically an embodiment comprising a DC-connected gen set, suchas in FIG. 5B. The modes are substantially the same as FIG. 9A with theaddition of mode H, block 3000. This additional H-mode is advantageouslyprovided to support a temporary AC-connection, FIG. 7B, for the gen set1032 in the event of a fault on the load side.

Following is a more detailed discussion of the various modes ofoperation illustrated in FIG. 9A and 9B. Section headings are intendedonly as a guide for the reader and are not to be understood in any wayas limiting the inventive concept, as information about various aspectsof the invention can be found throughout the sections and elsewhere inthis description.

Standby Mode (STATCOM Mode)

The standby mode step A (710), for example as shown in FIG. 9A, is thedominant operational mode for the power source system 220, during whichit acts as a STATCOM, keeping the load voltage within a narrow band. Thepower source system 220, for example, can maintain the load voltagewithin ±15% of the steady state load voltage, preferably within ±10% ofthe steady state load voltage, and more preferably within ±5% of thesteady state load voltage. The system 220 may also supply a small amountof real power to offset losses incurred by the storage unit 1000 and tomaintain the storage unit 1000, such as the battery 1060, at anappropriate energy, e.g., charge, level. During standby mode, the system220 is under current control (as designated in FIG. 9A by “IC” where theletter “I” designates current and the letter “C” control), and theinterconnected utility grid supplies the load and the system 220 acts asa current source.

During Stand-by operation mode, the energy storage module is maintainedat the desired state of charge. The VSC 240 provides real and/orreactive power to the system as required, or compensates for moderatevoltage fluctuations. The VSC advantageously maintains voltage at anoptimum level with reactive power generation or absorption and a smallamount of active power to compensate for the losses of the attachedenergy storage system.

Typically, during standby operation, the system 220 maintains energystorage module 1000, comprising in one embodiment battery 1060, FIG. 8A,at substantially a full charge. However, in another embodiment, storagemodule 1000 is maintained at less than full charge, for example 10% to20% below full charge (or at any other predetermined or dynamicallydetermined charge), to accommodate special operating modes such asoscillation damping on the grid 112. Alternatively or additionally, thecontrol system 221 allows for a constant load power factor, voltagespike protection, and harmonic cancellation.

In standby mode (block 710), for example as shown in FIG. 9A, the sagand outage detection unit 1080 acts as a watchdog to detect systemdisturbances. This may be performed by sensing the line-to-ground ACsystem voltages. In such a case the signals to be evaluated may includethe absolute values, the positive phase sequence component, the negativephase sequence component, and/or substantially any other metricindicative of AC system voltage such that the unit can quickly detect asupply voltage decrease/increase, a sudden increase in the negativephase sequence component, and steps or changes in phase angle. Fromthese circumstances, the sag and outage detection module 1080 coulddetermine that a system (grid) fault is present and initiate furtheraction. The control system discriminates between load side and systemside faults and initiates appropriate actions.

In one embodiment, the energy storage module 1000 comprises one or moreenergy storage components or devices, or a combination of components forstoring energy including chemical storage cells, capacitors,electrochemical capacitors, superconducting magnetic energy storage(SMES), flywheels, compressed air energy storage (CAES), and/orsubstantially any other storage component known in the art. The storagedevice, such as battery 1060, is part of an energy storage system 1000.In one embodiment, the storage system 1000 further includes a voltagesource converter (VSC) 240 coupled with the storage device, e.g.,battery 1060, via an internal DC link or other link. The VSC 240 furthercouples with the grid 224 through a solid state breaker unit (SSB) 262.The VSC 240, as directed by the current control, is capable of drawingpower from the grid 224 (or a generator source described elsewhereherein and below) for charging the storage device, e.g., the battery1060, as well as supplying power to the load 222 from the storagedevice. The VSC 240 further maintains the voltage of the storage unit236 at an optimum or near-optimum level with absorption of active powerto compensate for the losses of the attached energy storage device 1000.In one embodiment, a storage control unit 247 and an optional DC linkvoltage control, FIG. 8A, are utilized to match the terminalcharacteristics of the storage unit 1060 (voltage, current, and/orfrequency) with the requirements of the VSC DC link, typically dependenton the electrical behavior of the storage device implemented.

STATCOM operation is available in standby mode, in part, through aQ-controller 242 which aids in the control of the reactive powerprovided to/from the VSC 240. The Q-controller 242 couples with areference value generator 248 which supplies an amplitude reference loadvoltage V_(L,abs)* where the subscript “L,abs” is indicative of anamplitude of the load voltage. In the description provided here, theasterisk “*” indicates a reference or set point voltage or current and avoltage or current without the asterisk “*” indicates a related actualor sensed voltage or current. Q-controller 242 is further coupled withthe converter current controller 230. Based on a comparison between thereference amplitude load voltage V_(L,abs)* and the feed back of theamplitude of the load voltage V_(L,abs), the Q-controller generates areference converter reactive current I_(B)* which is supplied to thecurrent controller 230. The actual reactive converter current I_(B) isfed back to the converter current controller 230, where, in oneembodiment, the reactive converter current I_(B) is proportional toconverter reactive power as compensated by the VSC 240.

In one embodiment, the output of the converter current controller 230 isconnected to the pulse pattern generation unit 252. The pulse patterngeneration unit 252 is connected to a gate drive unit (GDU) 253 in theVSC 240, where the pulse patterns are transformed into gate drivesignals of the VSC 240. The pulse pattern generation unit 252, throughthe GDU, switches or triggers on and off the power semiconductors in theVSC 240. By controlling the time that each power semiconductor in theVSC conducts, both the magnitude and the phase angle of the resultingVSC AC output voltage are controlled. This provides independent controlfor both active and reactive power. Embodiments of the invention providedifferent or combinations of control, such as providing a pulse patterngeneration unit 252 that generates pulses according to pulse widthmodulation techniques (PWM methods), modified PWM methods, optimizedpulse pattern techniques (OPP methods), or substantially any other pulsemodulation technique known in the art, extensions of such techniques ornew techniques developed in the future. The choice of pulse modulationor pulse pattern technique may typically be dictated by the type ofsemiconductor used in the VSC, switching frequency, and the objectivesof harmonic elimination and reduction of total harmonic distortion (THD)or the like factors or combinations thereof.

In one embodiment, the pulse pattern generation unit controls the VSC240 such that the actual converter reactive current I_(B) exchanged(i.e., current injected or absorbed) follows the value set by thereference converter reactive current I_(B)*. Injection or absorption ofreactive current acts to control the amplitude of the load voltage,V_(L,abs), to the desired set point value V_(L,abs)*. Reactive powerflow is controlled by the magnitude of the VSC AC (fundamental) voltagerelative to the magnitude of the load (or system) AC voltage V_(L,abs).If the VSC voltage is less than the load voltage, the converter absorbsreactive power. Conversely, if the VSC voltage is higher than the loadvoltage, the VSC injects reactive power.

The utilization of VSC 240 as a STATCOM, as well as addition of energystorage systems connected to the VSC DC-link requires in most cases a DClink voltage controller (see, for example, FIG. 8A, 13A, and 13B). TheDC link voltage controller operates advantageously to keep the DC linkvoltage constant and compensate for internal losses.

In one embodiment, in which a SMES is utilized as the energy storagemodule 1000, FIG. 13A, the DC link voltage controller 4030 operatesadvantageously to maintain DC link voltage by means of discharging orcharging the magnet via a DC Chopper (DCC). In one implementation ofthis embodiment, the DC link voltage controller 4030 adjusts the inputI_(DC)* of the pulse pattern generation unit 4040 of the DCC, such thatthe DCC discharges or charges the magnet to restore the DC link voltage.

In another embodiment, in which a flywheel is utilized as the energystorage module 1000, FIG. 13B, the DC link voltage controller operatesadvantageously to control the VSC DC link voltage by generating areference current I_(W)* by comparing voltage V_(DC) with the referencevoltage V_(DC)*. The flywheel speed is also kept constant during standbyby the flywheel charge control 5061.

In one embodiment, an exception to the requirement for a DC link voltagecontroller may be realized when the storage module 1000 comprises achemical battery 1060. In one implementation of this embodiment, theDC-link voltage is defined by the voltage and current (V/I)characteristic of the battery. A DC-link voltage is applied to a batterymanagement system 243 which provides a reference DC-link voltage V_(DC)*to a battery voltage control unit 244. The battery voltage control unitfurther receives the DC-link voltage V_(DC) for comparing the DC-linkvoltage V_(DC) and the reference DC-link voltage V_(DC)*. The batterymanagement system 243 couples with a battery current control unit 245,and supplies a reference DC-link current I_(DC)* to the battery currentcontrol unit 245. The battery current control unit 245 further receivesa DC-link current, and generates a setpoint reference active currentI_(W)* based on the comparison between the reference DC-link currentI_(DC)* and the DC-link current I_(DC). Both the battery voltage controlunit 244 and the battery current control unit 245 couple with a switch246 which is controlled by the battery management system 243 dependingon the mode of operation to provide at least the reference activecurrent I_(W)* to the VSC current control 230.

An active current I_(W), proportional to the active power exchanged withthe system through the VSC 240, and a reactive current I_(B),proportional to the reactive power exchanged with the system, are alsofed back to the converter current controller 230. Based on comparisonsbetween the reference reactive converter current I_(B)* and the reactiveconverter current IB, as well as between the reference active currentI_(W)* and active current I_(W), the current controller 230 controls theVSC 240 to exchange active power with the storage unit 236, to maintainits charge, and/or to exchange reactive power with the storage unit(STATCOM operation).

The output of the converter current controller 230 is coupled with thepulse pattern generation unit 252. The pulse pattern generation unit252, in one embodiment, triggers drive circuits of power semiconductorof the VSC 240, as described above, dictated by the converter currentcontroller output.

FIG. 10 depicts a simplified block diagram of one embodiment of theconverter current controller 230. In another embodiment, the currentcontroller is a standard closed loop controller, as known in the art. Inone embodiment, the VSC current control 230 is composed of twoProportional Integral (PI) type feedback control circuits, a firstcontrol circuit 516 computing the active component Y_(W) and a secondcontrol circuit 518 computing the reactive component Y_(B) of thecurrent. In one embodiment, the space vector theory is used to derivethe real and reactive current components. Space vector theory, as knownin the art, allows one to describe three linearly dependent quantities,such as, three voltages or three currents, in the generalized form ofclassical phasor representation, by using only two linearly independentquantities represented in an orthonormal coordinate system. The voltagedrop of the VSC transformer is calculated via pre-control. The VSCcurrent controller is disabled 519 in discharge mode.

In one embodiment, a requested converter current vector (outputted fromthe converter current controller) is translated into a pulse pattern bythe pulse pattern generator by means of a PWM (pulse width modulation)trigger set or other such trigger-sets including optimized pulse pattern(OPP) trigger-sets.

The trigger set is a means to generate power semiconductor individualtrigger signals. In one embodiment, permanent pulses are used, with apulse length equivalent to the expected conduction period of theindividual switch. Electrical potential de-coupling may be obtained byapplying optocouplers and fiber optics or other isolation means. In oneembodiment, individual switch interlocking (to consider minimum “on”times and minimum “off” times and prevent a short circuited DC linkcapacitor) is utilized.

Discharge Mode (Island Mode, Storage Conditioning)

During the operation of power source system 220, a sag and outagedetection and mode selection unit 1080 monitors the grid 224 for powerfaults, such as, voltage sags, interruptions, outages and other suchfaults. The outage detection and mode selection unit 1080 furtherdetermines where the fault is located (i.e., the grid side or the loadside). The detection and mode selection unit 1080 couples with a gridSSB or switch 262. In the event the detection and mode selection unit1080 detects a fault on the grid, the detection and mode selection unitopens the grid SSB 262 disconnecting the grid from the load. The controlsystem 221 transfers power source system 220 into discharge mode in stepB (712) after a sag or outage has been detected and the disturbed grid112 has been disconnected, that is SSB 262 has been opened. The system220 may utilize a series reactor between the VSC 240 and the load bus,or in other configurations as known in the art, such as a duplexreactor, in order to allow for current injection during the periodbetween fault initiation and SSB 262 opening. Further, the detection andmode selection unit 1080 couples with and activates the convertervoltage controller 232 in the event a fault is detected on the grid 224.The detection and mode selection unit 1080 further signals to deactivatethe converter current controller 230. The converter voltage controller232 signals the pulse pattern generation unit 252 which activates theVSC 240 and storage unit, such as battery 1060, to take over and supplyfull power to the load. Subsequent to opening of the SSB (isolation ofthe load from the grid) the system 220 begins operating as a voltagesource. During transfer period 712 the control system 221 allows forthis transition from current control (IC) to voltage control (VC).

For example, after fault detection, the SSB is opened withinapproximately 4 ms or other suitable time period at which point thecontrol shifts from current to voltage control. Following the opening ofthe SSB, the power supplied by the system 220 is built up to a stablelevel within the time period (approximately 4 ms). The time of 4 msprovides for advantageous implementation of power system 220, however,any other timing values may be utilized. For example, a time period ofbetween 1 ms or less and about 20 ms may frequently be used though timesof between 4 ms and 8 ms are more usual, as well as other timing values.(FIG. 14 describes data for a 6 ms time period.)

Discharge mode is entered in step C (block 714), where the actual loadduring discharge mode defines the amount of power to be drawn from thestorage source 1060. The duration of discharge is dependent on theenergy content of the storage unit 1060. Before the storage unit isexhausted the control system 221 transfers the load to the alternativepower source (if provided) or shuts down the load. In discharge mode C(block 714), the system determines whether the grid has stabilized andthe fault continues to exist. If the fault no longer exists andpredefined conditions are meet (i.e., the grid is stable for apredefined period of time), the system transitions back to normaloperating conditions, normal operating mode A (block 710). If the faultcontinues, a switch-over to alternative power source mode D (block 716)is entered where the system 220 begins a transition to the alternatepower generation source (gen set) mode. The detection and mode selectionunit 1080 is capable of activating the alternative power source on thebasis of storage-related factors (such as for example, remaining storagetime), generator start up times, and/or other parameters. The controlsystem allows for computing suitable transfer parameters from eithermeasured or characteristic (fixed) data. The system 220 prevents thestorage unit 1000, such as battery 1060, from operating in an unsafemanner (e.g., outside its operational envelope).

In discharge mode B, the control strategy has changed from a current orpower control mode to a voltage control mode dictated by the convertervoltage controller 232. Under island discharge conditions (i.e., loadisolated from the grid) the load 222 defines the reactive and activepower. Both reactive and active power are supplied by VSC 240 andstorage unit, battery 1060. The converter voltage controller 232receives a reference load active voltage V_(LW)*, and at least the loadactive and reactive voltages V_(LW), V_(LB) are fed back to theconverter voltage controller 232. The converter voltage controllercontrols the VSC and storage unit based on the load active and reactivevoltages through the pulse pattern generation unit 252. One advantage ofapplying reactive and active power through the VSC is that the VSCsignificantly reduces frequency variations due to load switching.

FIG. 11 depicts a simplified block diagram depicting one implementationof one embodiment of the converter voltage controller 232. In oneembodiment, the converter voltage control 232 is a standard closed loopcontroller, as known in the art. In one embodiment, the convertervoltage control 232 is composed of two PI-type feedback controlcircuits, a first control circuit 508 computing the active componentE_(W)* and second 510 computing the reactive component E_(B)* of thevoltage. Again, space vector theory may be used to derive the real andreactive voltage components. Through a pre-control the voltage drop of aVSC transformer is calculated. The converter voltage controller 232 isdisabled 512 in standby and charge modes. In these modes the loadvoltage V_(L) is simply switched directly to the output, where it isadded to the output of the current controller and is used as pre-controlin standby and charge mode. During discharge mode the load voltage V_(L)is controlled to its reference value to compensate the voltage drop overthe VSC transformer. In resynchronization mode the reference value ofthe voltage controller is the grid voltage V_(N).

FIG. 12 depicts a block diagram of one implementation of one embodimentof the detection and mode selection unit 260 which detects gridconditions and determines the mode of operation. The detection and modeselection unit detects grid faults and voltage dips (single phase aswell as two or three phase dip conditions). After detection of anabnormal grid condition the detection and mode selection unit activatesthe SSB 262 to disconnect (solid state breaker trigger signal) 608 thefaulty source from the load. The detection and mode selection unit 260further signals the energy storage unit, in one embodiment battery 1060,to build up load voltage by utilizing the VSC capabilities (via thevoltage controller 232) to transfer real power to the load.

The detection and mode selection unit 260 also reactivates 610 thestandby mode if the grid returns to normal levels, and also signalsresynchronization 612 if desirable from system conditions.

The detection circuit 620 utilizes the amplitude of the system voltages,voltage (V_(N,abs)). In one embodiment, the amplitude is obtained fromtwo linearly independent components resulting from the application ofthe space vector theory. In one embodiment, the detection and modeselection unit has three levels with graded reaction times according tothe Computer and Business Equipment Manufacturers' Association (CBEMA)or Information Technology Industry Council (ITI) curve. The accompanyingTable 1 illustrates some of the values requested by the CBEMA (ITI)curve. For example, if the supply voltage magnitude sags to 70% ofnominal for 1.2 cycles or longer, then the detection unit initiates anevent whereby the SSB 262 is activated to disconnect the grid from theload and the energy storage unit, in one embodiment battery 1060, isutilized by the VSC 240 to restore voltage to normal levels. Othervalues, rules, or policies may be implemented in the control scheme.TABLE 1 Requested ride through according to CBEMA (ITI) Supply voltagemagnitude rms (% of nominal) Time duration [60 Hz cycles] 0 Up to 1.2 70Up to 30 80 Beyond 30Charge Mode

Charge mode refers to recharge storage either in island mode or if theload is connected to the grid, or to storage conditioning. With furtherreference to FIGS. 9A and 9B, in step G (block 724), the control system221 transfers the system 220 into charge mode and carries out a rechargeof the energy storage system, for example battery 1060 after nominalcompletion of the discharge event. The storage unit supplier typicallyspecifies charging algorithms. Charging algorithms are usually specificto the particular energy storage module 1000 and are known in the art.

Recharging may occur either during island operation, sourced by thealternative gen set, or after return to normal grid operation, or both,as depicted in block 724 of FIGS. 9A and 9B. The control system 221hardware and software and method generally, allow flexibility toimplement different charge scenarios. For example, if the alternativesource 1030 is sufficiently sized in comparison to the load 222, it maybe desirable to partly or fully charge the storage system 1000 duringisland operation (block 720 of FIGS. 9A and 9B), based on a set ofpre-programmed rules or policies. In this case the control system 221would monitor the existing load 222, the generator 1030 capacity and thestorage state of charge 1000 and decide when to utilize the excess powerof the alternative power source 1030. It is worth noting that the energystorage system 1000 is useful for load stabilization and may bedynamically charged or discharged during island operation.

When the system 220 is operating in the charge mode, the energy storageunit 1000 is recharged and the control system switches over to thestandby mode automatically. VSC 240 draws power from the grid 224 orgenerator 256 to be stored in the storage unit 1000. The implementationof control system 221 differs according to the specific attributes ofdifferent storage units, examples are shown in the accompanying Table 2.Below, specific exemplary embodiments of control system 221 arediscussed for three situations - when storage module 1000 comprises: (i)a chemical battery, (ii) a SMES, and (iii) a flywheel. It is to beunderstood by those workers having ordinary skill in the art in light ofthe description provided that similar embodiments may be implemented forother storage technologies, including but not limited to electrochemicalcapacitors and compressed air energy storage (CAES), and that theinventive concept, system, and method are applicable to a theseparticular storage technologies as well as to a variety of other energystorage technologies now existent or to be developed. TABLE 2 ControlSystem Modules Active for Storage Applications Battery SMES FlywheelControl Mode Automatic x x x VSC Current Controller x x x VSC VoltageController x x x Battery Management Voltage and x Current ControllerMagnet Current Controller x DC link Voltage Controller x x GeneratorExcitation Control x Setpoint Generation unit x x Rectifier voltagecontrol x Pulse Pattern Generation VSC x x x Pulse Pattern generationDCC x Flywheel charge control x DC Chopper control x

First, we turn to the case where storage module 1000 comprises anelectro-chemical or other chemical storage, such as battery 1060. Thisembodiment is illustrated in FIGS. 8A and 8B with and AC-connected orDC-connected gen set, respectively representing generation module 1030.Briefly, the basic building block of a battery module is anelectrochemical cell. A single module may have one or more cells inseries, in parallel, or in series/parallel combination. A battery stringor array may be a series connection of several battery modules to obtainthe needed battery voltage suitable for the power conversion systems.Strings may be paralleled to gain the desired energy or energy capacity.The most commonly used battery type is the lead-acid (Pb-acid) type.Other technologies like Sodium Sulphur, Sodium Polysulfide, VanadiumRedox, or Zinc Bromine are emerging for energy storage applications, andmay be utilized as battery 1060. The voltage of a Pb-acid cell typicallydecreases as the discharge progresses. Manufacturers typically specifyan end of discharge (EOD) voltage or cut off voltage. Therefore for aconstant power discharge the current is highest at the end of discharge.

The DC-link voltage is defined by the voltage and current (V/I)characteristic of the battery. A battery management system 243 isadvantageously added to control recharge of the battery. Batterycharging is assumed to take place in two or more constant current orconstant voltage steps. The process is sequential and change-over to thenext step occurs when a specified current or voltage is reached.Depending on the charge state of the battery the current or the voltageof the battery and accordingly the voltage of the DC-link is controlled.The output of the battery voltage controller 244 or of the batterycurrent controller 245 is switched to provide the input I_(W)* to theVSC current controller 230, which sets VSC active power output. For bothcharge and discharge the VSC active power establishes the batterycurrent and, via voltage-current characteristic, the battery voltage. Indischarge mode the battery management system 243 and the VSC currentcontroller 230 are disabled, and I_(W) is determined by the load.

Thus, when storage module 1000 comprises a chemical battery, such asbattery 1060 in FIGS. 8A and 8B, the battery management system 243 incooperation with the battery voltage control 244 determines that thevoltage level of the storage system has fallen below a predefinedthreshold. The battery voltage control 244 signals the converter currentcontroller 230 to charge the storage unit 1000, battery 1060. Thecurrent controller 230 signals the pulse pattern generator unit 252which in turn activates the VSC 240 to draw power from the grid orgenerator and charge the storage unit 1000, battery 1060.

Another embodiment is shown in FIG. 13A, where a SMES is utilized forenergy storage. For simplicity, generation system 1030 and associatedcontrols are not shown in FIG. 13A. It is to be understood that ageneration module, such as an AC- or DC-connected gen set may beutilized along with storage module 1000 comprising SMES. The storedenergy (E) in a SMES is proportional to the SMES coil inductance (L)multiplied by the square of the coil current (I), or E=½ LI² where theproportionally constant here is ½.

Briefly, SMES, as a magnetic energy storage system, can be treated as acurrent source which can be transferred into a voltage source bychopping its DC-current (by means of an extra device, such as a DCchopper) and charging and discharging its DC-Link capacitor consideringacceptable DC-Link voltage ripple. The magnetic field created by theflow of direct current in a coil of superconducting material storeselectrical energy. As energy is removed from the SMES, the coil currentdecreases. To maintain the coil in its superconducting state, it isimmersed in liquid helium contained in a vacuum-insulated cryostat.Typically, the coolant is liquid helium at 4.2 K (4.2 Kelvin) orsuper-fluid helium at 1.8 K (1.8 Kelvin). Large SMES systems beyond 10MW with storage times of several minutes are under development and maybe utilized. Their design is based on low temperature superconductors(LTS), for example niobium-titanium. Such systems may advantageously beutilized in storage module 1000. SMES systems are still in adevelopmental stage, though systems are becoming commercially available.

Referring to FIG. 13A, charging and discharging of a SMES requires a DCChopper 4000 (DCC) to be connected between the superconducting magnet4010 and the DC link circuit of the VSC. As shown in FIG. 13A the energystorage control module 2000 comprises the SMES charge control 4020, theDC link voltage control 4030, and the pulse pattern generation unit4040.

In charge mode (block 724 in FIG. 9A) and standby mode (block 710 inFIG. 9A), the magnet current I_(Mag) is controlled by the energy storagecontrol module 2000. The SMES charge controller 4020, the Q-controller242 and the VSC current controller 230 are disabled in discharge mode(block 714). The DC link voltage V_(DC) is controlled by the DC linkvoltage controller 4030 in all control modes. In this mode, that isduring operation of the VSC 240 to mitigate a sag or outage, energy isdrawn from the DC link capacitor causing the DC link voltage to drop.However the DC link voltage controller 4030 attempts to maintain the DClink voltage by adjusting the input I_(DC)* of the pulse patterngeneration unit 4040 of the DCC, such that the DCC discharges the magnetto restore the DC link voltage.

Charging the magnet is the reverse process of the above mentioned. Theoutput of the DC link voltage controller 4030 is connected to inputI_(DC)* of the pulse pattern generation unit 4040 of the DCC. Themodulation factor defines the power flow from the magnet to the DC linkor vice versa. In charge mode the reference value I_(W)* (which isproportional to the required magnet charging power) depends on the SMEScharacteristic implemented in the SMES charge controller. In standbymode, the reference value I_(W)* is theoretically zero, but in practicalterms due to standby losses there will typically be some continuous lowlevel charging.

In yet another embodiment, as shown in FIG. 13B, a flywheel is utilizedfor energy storage. For simplicity, as with FIG. 13A, generation system1030 and associated controls are not shown in FIG. 13B. It is to beunderstood that a generation module, such as an AC- or DC-connected genset may be utilized along with storage module 1000 comprising aflywheel. Briefly, a rotating flywheel as a kinetic energy storagesystem can act as a prime mover for a generator. Therefore, a flywheelutilized as an energy storage device may also serve as part ofgeneration module 1030. The stored energy (E) in flywheels isproportional to the flywheels moment of inertia (J) multiplied by thesquare of its angular speed (W), or E=½ JW² where the proportionallyconstant here is ½. Because of the square dependency (like SMES) and theadvent of new composite materials with high tensile strength, highvelocities are attractive to store large amounts of energy. Recentdevelopments report attainable angular speeds from several tens ofthousands up to 100,000 revolutions per minute. Similar to SMES, asenergy is removed, the speed decreases. Flywheel energy storage systemsare still in a developmental stage, though systems are becomingcommercially available. Flywheels in the several tens to severalhundreds of Megajoules range (1 MJ=1 MW-sec) are available in both theslow running steel type wheels, as well as in the newer glass fibercomposite wheels operating at high speeds.

The conversion of kinetic energy to electrical energy requires anelectrical generator (storage discharge). Typically an AC generator 5010is applied and produces an output frequency which varies with the(decreasing) speed of the flywheel. For conversion of electrical energyto kinetic energy an electrical motor 5020 is required to facilitatestorage charge capabilities.

For charging and discharging of a flywheel, a motor/generator unit or agenerator with a separate pony motor is used, as known in the art. Byutilization of an additional rectifier 5030 between the VSC 240 DC linkcircuit, and the generator unit, the speed (frequency) dependency of theflywheel output can be de-coupled in what may be referred to as aclassical back-to-back arrangement.

In contrast to SMES and battery, system discharging and chargingcontrols may typically be implemented by separate systems. As shown inFIG. 13B, the flywheel energy storage control module 2000 comprises atleast a DC link voltage control, a current control and a rectifier pulsepattern generation unit 5050. The control system 221 and method providesfor input of flywheel status signals such as operating speed. For theflywheel, a generator excitation control 5040 and a motor controlsubsystem 5060 (comprised of a flywheel charge control 5061 and motorcontrol unit 5062) are also usually deemed necessary and may or may notbe supplied with the flywheel. Thus, optionally, storage control module2000 may also comprise one or more units of the flywheel motor/generatorcontrol package 5070, FIG. 13B, depending on the extent of the controlsimplemented by the flywheel manufacturer. In discharge mode, theflywheel generator is connected to the DC link via a controlledrectifier 5030. The controlled rectifier bridge is gated by therectifier control 5050 trigger set in such a manner that the rectifiedgenerator current flows into the DC link, maintaining the DC-linkcapacitor voltage. For charging the flywheel 5000, a pony motor 5020 isused to restore the flywheel speed to its nominal value (stored energyis proportional to angular velocity squared). This is achieved by meansof the flywheel charge control 5061 through the motor control unit 5062.The output of the charge controller 5061 represents the pony motortorque reference value. In standby mode the flywheel speed is also keptconstant or at some designated speed by the flywheel charge control5061, in order to overcome windage, friction, and other standby lossesin the rotating machine.

As described above, the SMES-specific controllers and theflywheel-specific controllers are optionally plug-and-play modules thatmay be interchanged or adapted as needed. Thus, if the battery 1060 inthe system is replaced by another energy storage device, such as an SMESdevice, the battery energy storage control module may be replaced(either with a new hardware and software control module or byreprogramming the control module) with an alternative energy storagecontrol module that includes the SMES-specific controllers.

Gen Set Start Up

Returning to a general discussion and specifically referring to theexemplary embodiment of power source system 220 depicted in FIGS. 8A and8B as well as the embodiment of the various modes illustrated in FIGS.9A and 9B, if a grid fault is detected and continues, step D (block 716)is entered where system 220 begins a transition to the alternate powergeneration source mode.

The control system 221 and method provides for input of generator statussignals such as achievement of stable nominal operating speed. Afterthis information is received ramp up of the gen set (to take over theload) may start. Due to increase in DC link voltage, the energy drawnfrom the battery 1060 ramps down as the gen set 1031 or 1032 ramps up.During this transfer period the control system 221 provides load sharingbetween multiple energy sources for the purpose of obtaining a smoothtransfer (for example, by minimizing both duration and magnitude ofvoltage and frequency oscillations).

In step E (block 720), the system 220 transitions to the gen set modeand the control system 221 allows for continuous operation of thealternative power source 1030 until the grid 224 returns or thealternate power source can no longer supply power (for example, ifgenerator fuel is exhausted). During alternative power source operation,the system 220 provides for load sharing between multiple energy sourcesto at least maintain load frequency and voltage within an acceptableband.

In one embodiment, the system 220 provides suitable alarms to indicatethat a safe shut down of the protected load (or process) is necessarydue to end of storage reached, fuel exhausted, or other situationendangering sensitive load 222 or in response to other concerns orcriteria.

It should be noted that, with implementations of power system 220 with aDC-connected gen set 1032, for load side short circuits special casesexist which may require transfer from a DC connection of the Gen set toan AC connection, represented as block 3000 of FIG. 9B. This effect,known as ‘insufficient short circuit power (on load side)’, can bemitigated by temporarily rearranging the Gen set connection (from DC toAC) via an additional SSB 1035 (FIG. 7B) to allow for fault clearingcontribution in load side breakers and/or fuses. Control system 2000,through the sag and outage detection module 1080, advantageouslymonitors load side voltage and current parameters so as to determine theevent of a load side fault requiring generator reconfiguration, andprovides the required signals to activate switch over from DC to ACconnection, and return to DC connection when conditions warrant.

When the grid (voltage and frequency) returns to a normal range or levelstep F (block 722) is entered and the system 220 transfers the load fromthe alternative source to the grid. In one embodiment, the controlsystem advantageously but optionally ensures that the generator 1030operates for a minimum period of time after a start to allow themechanical system to reach stable operating temperature. During thistime frame, the energy storage unit 1000 may be recharged.

Referring back to FIGS. 8A and 8B, in one embodiment, following thedetection of a power fault on the grid 224, the detection and modeselection unit 1080 further activates the gen set 1031 or 1032, suchthat the gen set 1031 or 1032 provides longer term power to load 222, asdiscussed above. Generation module 1030, more generically, representssubstantially any power generation source such as a motor or engine incombination with a power generation process, and substantially any otherpower generation source or combination known in the art. In oneembodiment, the gen set 1031 or 1032 is activated if the energy contentof the storage unit 1000 is below a predefined threshold. In oneembodiment, the gen set 1031 or 1032 is not activated until the fault isdetected on the grid for a predefined period of time. The detection andmode selection unit 1080 signals a power generation control unit 2010which initiates the gen set. The gen set speed n ramps up, while the VSC240 and storage unit 1000 continue to supply power to the load. The genset speed n is continued to be controlled by the power generationcontrol unit 2010. In one embodiment, the gen set includes a fuelinjection system 554 which determines the torque of the gen set. Theamplitude of the generator output voltage V_(Gen,abs) is controlled by agenerator excitation control unit 282.

Referring back to FIG. 8A, in one embodiment, the power source system220 includes a generator, such as a diesel gen set, connected to theload. The structure of the block diagram shown in FIG. 8A includes thestructure of the generator control topology with energy storage.

After the detection and mode selection unit 1080 has caused the SSB 262to open in the event of a grid fault, the diesel start/stop unit 550 ofthe power generation control unit 2010 starts the generator and thegenerator speed n ramps up, while the storage unit 1000, comprisingbattery 1060, supplies the load. The VSC current controller 230 isdisabled. The generator speed n is controlled by the generator controlsystem 552 which is part of the power generation control unit 2010. Thefuel injection system 554 determines the torque of the generator. Theamplitude of the generator output voltage V_(Gen,abs) is controlled bythe generator excitation control 282.

Once the gen set 1031 is activated, and the gen set output has reached asufficient level, the generator output voltage V_(Gen) is synchronizedwith the load voltage V_(L) supplied by the VSC 240 and storage unit1000. In synchronizing, a synchronizing unit 284 receives the loadvoltage V_(L) and the generator voltage V_(Gen) such that thesynchronizing unit 284 signals the detection and mode selection unit1080 to connect the gen set 1031 to the load 222 to supply power to theload. When the generator output voltage V_(Gen) has been synchronized tothe load voltage V_(L) a generator switch 286 is activated by the powergeneration control unit 2010 to close, connecting gen set with the load.In one embodiment, to gain an optimized (smooth and/or bumpless)takeover from the discharge mode without the gen set, to the gen setforming the primary power source, the control system 221 provides a loadsharing which ramps the active power output of the VSC 240 and storageunit 1060 down as the output from gen set 1031 ramps up. As the powersupplied by the gen set ramps up, the converter current controller 230signals the pulse pattern generation unit 252 to ramp down the powersupplied by VSC 240 and supply system 1000, in FIG. 8A comprisingbattery 1060.

When the generator output voltage is synchronized through thesynchronizing unit 284 with the load voltage V_(L), the generator switch286 is closed, and the operation mode is switched to standby mode. TheVSC current controller 230 and Q-control 242 are enabled. The VSCvoltage controller 232 is disabled. The VSC current controller 230 rampsthe VSC active power down as the gen set 1031 ramps up and takes overthe load.

STATCOM operation of the VSC improves the stability of the load voltage.While the Gen Set 1031 supplies the load, at least two different methodsof VSC control are possible in dynamic cases. In one embodiment, the VSC240 takes over no active power at any time. In an alternativeembodiment, the VSC takes over a part of the active power. The lattercase is possible if there is sufficient storage capacity in the storageunit 1000, comprising for example battery 1060.

Battery charging is possible during gen set operation. Moreover this isbeneficial when the generator is implemented through a diesel enginebecause diesel engines should be operated (at least from the standpointof engine longevity) until reaching nominal operating temperaturesbefore being shut down.

The detection and mode selection unit 1080 continues to monitor the gridduring each mode of operation, including gen set, UPS and STATCOM modes.After the grid voltage V_(N) has returned to normal operating ranges,the gen set 1031 is synchronized to the grid voltage V_(N). If the loadvoltage V_(L) is synchronized to the grid voltage V_(N) the detectionand mode selection unit 1080 closes the SSB 262. The grid 224 takes overthe load, the generator start/stop unit 550 ramps down the fuelinjection of the generator, and the generator switch 286 is opened. Inone embodiment, STATCOM mode is entered to continue to provide staticcompensation.

Parallel Operation Gen Set and UPS

When the generator switch 286 has been closed the converter currentcontroller 230 and the Q-controller 242 are also activated, and theconverter voltage controller 232 is deactivated. Thus, the controlshifts from a voltage control to a current or power control. The loadvoltage V_(L) is determined by the gen set 1031 with active assistancefrom the VSC 240 and storage unit 1000, comprising for example battery1060. The active and reactive power P_(W), Q_(B) of the VSC 240 arecontrolled through the converter current controller 230. The batterymanagement system 243, battery voltage control 244 and battery currentcontrol 245 aid in controlling the load sharing between the UPS and thegen set under dynamic (transient) conditions, thereby enhancingstability of the load.

The converter current controller 230 slowly ramps the converter activepower P_(W) supplied by the storage system 1000 down as the gen set 1031takes over the load 222. In one embodiment, under steady stateconditions, the UPS (typically including, but not limited to orrequiring, VSC 240, battery 1060, battery management system 243, andcontrollers 230, 242, 244, 245, 252 and 260) does not provide activepower. The VSC 240 provides reactive power Q_(B) to the load 222 asneeded thus continuing to providing STATCOM functionality. With theSTATCOM functionality and control, operational stability of the loadvoltage V_(L) is enhanced.

Under steady state conditions the gen set provides the active power forthe load 222. In one embodiment, under dynamic conditions, due to therelatively slow speed control of an electromechanical system incombination with the power generation process, the speed of the systemmay vary in a wide range. Therefore; dynamic frequency variations mayoccur. The UPS, including VSC 240 and storage unit 1000 with its shortresponse time, minimizes or attempts to minimize frequency fluctuationsby injecting or absorbing active power. In one embodiment, due to thelimited storage of the storage unit 1000 the UPS controls the averageamount of active power to substantially zero.

Transfer to the Grid

While operating to supply the load through the UPS or the gen set, thedetection and mode selection unit 1080 continues to monitor the grid 224to determine if the grid voltage V_(N) has returned to substantiallynormal levels. In one embodiment, transition to the grid occurs afternormal levels are detected. Once the power fault on the grid disappearsand the grid voltage V_(N) returns to normal levels the gen set voltageV_(Gen) and the load voltage V_(L), are synchronized to the grid voltageV_(N). The synchronization unit 284 receives the gen set output V_(Gen),load voltage V_(L), and the grid voltage V_(N). The synchronization unitsignals the detection and mode selection unit 1080 to provide controlsignals to the current and/or voltage controllers 230, 232 to adjust thegen set and/or VSC such that the load voltage V_(L) synchronizes withthe grid voltage V_(N). Once the load voltage V_(L) is synchronized tothe grid voltage V_(N) the detection and mode selection unit closes thegrid switch 262 again coupling the grid with the load. The detection andmode selection unit 1080 in combination with the reference valuegenerator 248 ramps down the VSC 240 and/or fuel injection 280 and thusthe gen set 1031 through the generator excitation controller 282. Theload sharing transitions the power supply from the gen set 1031 and/orVSC 240 to the grid 224, where the grid takes over the load 222 andgenerator switch 286 is opened. The system 220 then returns to standbyor charge mode as described above.

FIGS. 14A-E depict graphical representations of the operation of anembodiment of the system 220 with the VSC 240 and storage unit 1000being activated to compensate for a sag on the grid 224 at time t=50 ms.FIG. 14A shows a graphical representation of the three phase gridvoltage V_(an)-V_(cn), with the voltage sag at t=50 ms. FIG. 14B showsthe graphical representation of the three phase load voltageV_(al)-V_(cl) during the voltage sag. Note that the sag in the loadvoltage is compensated for within approximately 6 ms through the VSC 240and storage unit 1000. FIG. 14C depicts a graphical representation ofthe amplitude of the grid voltage V_(absn) and the load voltage V_(absl)showing the system 220 rapidly responding the sag. FIG. 14D depicts agraphical representation of the three phase load currents I_(la)-I_(lc),and FIG. 14E depicts a graphical representation of the three phasecompensation currents supplied by VSC 240 and storage supply 1000 to theload 222.

FIGS. 15A-E depict graphical representations of the system 240 shiftingfrom the UPS mode to the gen set mode where the gen set takes over theload 222 during the sag conditions at t=100 ms. FIG. 15A graphicallyshows the load voltage V_(al)-V_(cl) as the voltage supplied to loadtransitions from the VSC 240 to the gen set. FIG. 15B graphicallydepicts the amplitude of the grid voltage V_(absn) and the load voltageV_(absl) as the gen set takes over and supplies power to the load 222.FIG. 15C graphically shows the three phase load current I_(la)-I_(lc) asthe gen set takes over. FIG. 15D graphically shows the three phase VSCcurrent I_(a)-I_(c) as the load sharing ramps down the VSC 240, and FIG.15E graphically shows the three phase generator current I_(aG)-I_(cG) asthe load sharing ramps up the gen set current supplied to the load tomaintain the load at a stable state. As seen in FIG. 15A, the loadvoltage decreases to approximately 85% and the generator excitationcontroller 282 takes approximately 150 ms to lift the load voltage. Inone embodiment, the STATCOM function of the VSC 240 is activated tomitigate this voltage decrease. (For demonstration purposes the STATCOMfunction was not activated during the generation of FIGS. 15A-E.)

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best use the inventionand various embodiments with various modifications as are suited to theparticular use contemplated. Having described the best mode, it isintended that the scope of the invention be defined by the claimsappended hereto and their equivalents.

1. An electrical power source system, comprising: an electrical powerstorage subsystem; and a control system coupled with the electricalpower storage subsystem, and configured to provide a plurality of modesof operation including at least a static compensator (STATCOM)operational mode and an uninterruptible power supply (UPS) operationalmode, and to control transitions between each of the plurality of modes,including operation in more than one mode at the same time.
 2. Theelectrical power source system as claimed in claim 1, wherein the staticcompensator (STATCOM) operational mode is implemented without aconventional static compensator (STATCOM), and the uninterruptible powersupply (UPS) operational mode is implemented without a conventionaluninterruptible power supply (UPS).
 3. The electrical power sourcesystem as claimed in claim 1, further comprising: an electrical powergenerator, wherein the control system is further coupled to theelectrical power generator, and is further configured to provide agenerator mode.
 4. The electrical power source system as claimed inclaim 3, wherein the control system is further coupled to the electricalpower generator and is further configured to provide a multiplicity ofgenerator connection modes, including at least a dc-connected generatormode and an ac-connected generator mode.
 5. The electrical power sourcesystem as claimed in claim 1, wherein: the control system is anintegrated closed loop control system.
 6. The electrical power sourcesystem as claimed in claim 1, wherein: the control system comprises: acurrent control system coupled with the electrical power storagesubsystem and the electrical power generator; and a voltage controlsystem coupled with at least the electrical power storage subsystem. 7.The electrical power source system as claimed in claim 6, wherein: thecurrent control system includes a voltage source converter (VSC) currentcontroller coupled with a pulse pattern generation unit; and the pulsepattern generation unit couples with the energy storage system and isconfigured to supply control signals to the energy storage system. 8.The electrical power source system as claimed in claim 7, wherein: thevoltage control system includes the VSC voltage controller coupled withthe pulse pattern generation unit; and the pulse pattern generation unitcouples with the energy storage system and is configured to supplycontrol signals to the energy storage system.
 9. The electrical powersource system as claimed in claim 8, wherein: the energy storage systemincludes a VSC coupled with an energy storage unit, wherein the energystorage unit is configured to store electrical energy, and the VSC isconfigured to draw energy from the energy storage unit and supplyelectrical energy to the energy storage unit.
 10. The electrical powersource system as claimed in claim 6, wherein: the control system furtherincludes a detection and mode selection unit coupled with the currentcontrol and the voltage control, and configured to determine the mode ofoperation of the apparatus.
 11. The electrical power source system asclaimed in claim 10, further comprising: a solid state breaker (SSB)coupled with the detection and mode selection unit and with a grid andconfigured to decouple a load from the grid; and the detection and modeselection unit is configured to signal the SSB to open and close. 12.The power system as claimed in claim 1, wherein the storage systemcomprises a battery.
 13. The power system as claimed in claim 1, whereinthe storage system comprises a flywheel.
 14. The power system as claimedin claim 1, wherein the storage system comprises an SMES.
 15. The powersystem as claimed in claim 1, wherein the storage system comprises anelectrochemical capacitor.
 16. The power system as claimed in claim 1,wherein the storage system comprises a compressed air energy storagesystem (CAES).
 17. The power system as claimed in claim 1, wherein thecontrol system includes at least one storage control module specificallyconfigured for controlling the operation of the electrical power storagesubsystem.
 18. The power system as claimed in claim 17, wherein thestorage control module is interchangeable with a second storage controlmodule that is specifically configured for controlling the operation ofa second electrical power storage subsystem.
 19. The power system asclaimed in claim 17, wherein the storage control module is chosen fromthe group comprising: a software configuration, a hardwareconfiguration, and a combination of a software and a hardwareconfiguration.
 20. The power system as claimed in claim 2, wherein thecontrol system includes at least one electrical power generator controlmodule specifically configured for controlling the operation of theelectrical power generator.
 21. The power system as claimed in claim 20,wherein the electrical power generator control module is interchangeablewith a second electrical power generator control module that isspecifically configured for controlling the operation of a secondelectrical power generator.
 22. An apparatus for providing electricalpower, comprising: a static compensator (STATCOM); an uninterruptiblepower supply (UPS); and a multimode control system coupled with theSTATCOM and the UPS, wherein the multimode control system is configuredto control the operation of each of the STATCOM and the UPS to cooperatethe STATCOM and the UPS to simultaneously provide reactive power (staticcompensation) and/or real electrical power in any combination before,during, and/or after a disturbance or outage on the electrical grid. 23.The apparatus as claimed in claim 22, further comprising: a generator,and wherein the multimode control system is further coupled with thegenerator, and wherein the control system is further configured tocooperate the generator with the STATCOM and the UPS to provide real andreactive electrical power.
 24. The apparatus as claimed in claim 23,wherein: the control system includes at least: a current control systemcoupled with the STATCOM, the UPS, and the generator, and configured toprovide control for the STATCOM, the UPS, and the generator; and avoltage control system coupled with at least the UPS, and configured toprovide control for the UPS.
 25. The apparatus as claimed in claim 22,wherein: the control system includes at least: a current control systemcoupled with the STATCOM and the UPS, and configured to provide controlfor the STATCOM and the UPS; and a voltage control system coupled withat least the UPS, and configured to provide control for the UPS.
 26. Theapparatus as claimed in claim 25, wherein: the control system includes:a detection and mode selection unit coupled with the current controlsystem and the voltage control system, and configured to signal thecurrent control system and the voltage control system to activate anddeactivate the current control system and the voltage control system.27. The apparatus as claimed in claim 26, wherein the STATCOM includesat least a voltage source converter (VSC) coupled with an energy storageunit, wherein the VSC provides at least static compensation (reactivepower injection/absorption).
 28. The apparatus as claimed in claim 27,wherein the UPS includes at least an energy storage unit but does notinclude a power conditioner, and wherein the UPS supplies power throughthe STATCOM from the energy storage unit.
 29. The electrical powersource system as claimed in claim 27, wherein the energy storage unit ischosen from the group comprising: a battery, a flywheel, an SMES, anelectrochemical capacitor, and combinations thereof.
 30. An alternatepower source system for coupling with at least one load and configurableto provide alternate electrical power to said at least one load, thealternate power source system comprising: a multimode control systemconfigured to cooperate a plurality of operational modes, the multimodecontrol system comprising: a current control system; and a voltagecontrol system.
 31. The alternate power source system as claimed inclaim 30, wherein the multimode control system is further configured toprovide multiple modes of operation including at least a standby modeand an energy storage discharge mode.
 32. The alternate power sourcesystem as claimed in claim 31, wherein the multimode control system isfurther configured to provide an energy storage charge mode, wherein thecharge mode is capable of operating during at least one of the othermultiple modes of operation.
 33. The alternate power source system asclaimed in claim 31, wherein the multimode control system is furtherconfigured to provide an alternate power source mode.
 34. The alternatepower source system as claimed in claim 33, wherein: the current controlsystem is configured to control at least an alternate power source modeof operation and a standby mode of operation; and the voltage controlsystem is configured to control at least an energy storage dischargemode of operation while the alternate power source mode is notoperating.
 35. The alternate power source system as claimed in claim 34,wherein the current control provides control for at least an energystorage discharge mode while the alternate power source mode isoperating.
 36. A method for supplying alternate power to a load,comprising: supplying power through at least one of a plurality of modesof operation, including a static compensation (STATCOM) mode and anuninterruptible power supply (UPS) mode; and controlling the pluralityof modes from a control system to cooperate the plurality of modes andto transition between the plurality of modes of operation.
 37. Themethod as claimed in claim 36, wherein the controlling further comprisesoperating simultaneously at least two of the plurality of modes ofoperation.
 38. The method as claimed in claim 37, wherein the operatingsimultaneously includes operating the STATCOM mode and the gen set modesimultaneously.
 39. The method as claimed in claim 36, wherein thesupplying power further includes a power generation (gen set) mode. 40.The method as claimed in claim 39, wherein the controlling furthercomprises operating simultaneously at least two of the plurality ofmodes of operation.
 41. The method as claimed in claim 40, wherein theoperating simultaneously includes: ramping the gen set mode up; andsimultaneously ramping the UPS mode down as the gen set mode is rampedup.
 42. The method as claimed in claim 40, wherein the operatingsimultaneously includes operating the gen set mode and the UPS modesimultaneously.
 43. A method for providing power to a load, comprising:operating an apparatus for providing power to a load including:operating in a standby mode; and operating in an uninterruptible powersupply (UPS) mode; and controlling the standby mode and the UPS mode tocooperate in providing substantially uninterruptible power to a load.44. The method as claimed in claim 43, wherein the operating theapparatus further comprises operating in a generator mode, and thecontrolling further includes controlling the generator mode to cooperatewith the standby mode and the UPS mode in providing the substantiallyuninterruptible power to the load.
 45. The method as claimed in claim43, wherein: the operating in the standby mode includes: monitoring agrid that supplies power to the load; and providing static compensation(reactive power injection/absorption).
 46. The method as claimed inclaim 44, wherein: the operating in the standby mode includes monitoringa grid that supplies power to the load; and the controlling includes:disconnecting the load from the grid if a fault is detected on the grid;and initiating the UPS to supply power to the load.
 47. The method asclaimed in claim 44, wherein: the operating in the generator modeincludes monitoring the load; and the controlling includes:reconfiguring the connection of the generator to the load from ac to dcconnection if a fault is detected on the load.
 48. The method as claimedin claim 46, further including: providing static compensation during theUPS mode.
 49. The method as claimed in claim 46, wherein: thecontrolling includes: initiating the generator mode and ramping up powersupplied through the generator mode; and ramping down the power suppliedthrough the UPS mode as the power supplied through the generator mode isramping up.
 50. The method as claimed in claim 49, wherein: thecontrolling includes: continuing to monitor the grid while operating inthe generator mode; synchronizing the power supplied through thegenerator mode if the fault on the grid is no longer detected;connecting the grid to the load; and halting the generator mode suchthat the power is no longer supplied to the load through the generatormode.
 51. The method as claimed in claim 46, wherein: the controllingincludes: continuing to monitor the grid while operating in the UPSmode; synchronizing the power supplied through the UPS mode if the faulton the grid is no longer detected; connecting the grid to the load; andhalting the UPS mode such that the power is no longer supplied to theload through the UPS mode.
 52. The method as claimed in claim 44,further comprising providing static compensation while operating in thestandby mode, the UPS mode, and the generator mode.
 53. The method asclaimed in claim 44, wherein the step of controlling includes chargingan energy storage system while operating in the standby mode and thegenerator mode.
 54. A computer program product for use in conjunctionwith a computer system having a processor and a memory coupled to theprocessor, the computer program product comprising a computer readablestorage medium and a computer program mechanism embedded therein, thecomputer program mechanism, comprising: a program module that directs apower system to supply alternate power (voltage and/or current) to aload, the program module including instructions for: supplying powerthrough at least one of a plurality of modes of operation, including astatic compensation (STATCOM) mode and an uninterruptible power supply(UPS) mode; and controlling the plurality of modes from a control systemto cooperate the plurality of modes and to transition between theplurality of modes of operation.
 55. A computer program product for usein conjunction with a computer system having a processor and a memorycoupled to the processor, the computer program product comprising acomputer readable storage medium and a computer program mechanismembedded therein, the computer program mechanism, comprising: a programmodule that directs a power system to supply alternate power (voltageand/or current) to a load, the program module including instructionsfor: operating an apparatus for providing power to a load including:operating in a standby mode; and operating in an uninterruptible powersupply (UPS) mode; and controlling the standby mode and the UPS mode tocooperate in providing substantially uninterruptible power to a load.